These routines open an SQLite database file as specified by the
filename argument. The filename argument is interpreted as UTF-8 for
sqlite3_open() and sqlite3_open_v2() and as UTF-16 in the native byte
order for sqlite3_open16(). A database connection handle is usually
returned in *ppDb, even if an error occurs. The only exception is that
if SQLite is unable to allocate memory to hold the sqlite3 object,
a NULL will be written into *ppDb instead of a pointer to the sqlite3
object. If the database is opened (and/or created) successfully, then
SQLITE_OK is returned. Otherwise an error code is returned. The
sqlite3_errmsg() or sqlite3_errmsg16() routines can be used to obtain
an English language description of the error following a failure of any
of the sqlite3_open() routines.

The default encoding will be UTF-8 for databases created using
sqlite3_open() or sqlite3_open_v2(). The default encoding for databases
created using sqlite3_open16() will be UTF-16 in the native byte order.

Whether or not an error occurs when it is opened, resources
associated with the database connection handle should be released by
passing it to sqlite3_close() when it is no longer required.

The database is opened for reading and writing if possible, or reading
only if the file is write protected by the operating system. In either
case the database must already exist, otherwise an error is returned.

The fourth parameter to sqlite3_open_v2() is the name of the
sqlite3_vfs object that defines the operating system interface that
the new database connection should use. If the fourth parameter is
a NULL pointer then the default sqlite3_vfs object is used.

If the filename is ":memory:", then a private, temporary in-memory database
is created for the connection. This in-memory database will vanish when
the database connection is closed. Future versions of SQLite might
make use of additional special filenames that begin with the ":" character.
It is recommended that when a database filename actually does begin with
a ":" character you should prefix the filename with a pathname such as
"./" to avoid ambiguity.

If the filename is an empty string, then a private, temporary
on-disk database will be created. This private database will be
automatically deleted as soon as the database connection is closed.

URI Filenames

If URI filename interpretation is enabled, and the filename argument
begins with "file:", then the filename is interpreted as a URI. URI
filename interpretation is enabled if the SQLITE_OPEN_URI flag is
set in the fourth argument to sqlite3_open_v2(), or if it has
been enabled globally using the SQLITE_CONFIG_URI option with the
sqlite3_config() method or by the SQLITE_USE_URI compile-time option.
As of SQLite version 3.7.7, URI filename interpretation is turned off
by default, but future releases of SQLite might enable URI filename
interpretation by default. See "URI filenames" for additional
information.

URI filenames are parsed according to RFC 3986. If the URI contains an
authority, then it must be either an empty string or the string
"localhost". If the authority is not an empty string or "localhost", an
error is returned to the caller. The fragment component of a URI, if
present, is ignored.

SQLite uses the path component of the URI as the name of the disk file
which contains the database. If the path begins with a '/' character,
then it is interpreted as an absolute path. If the path does not begin
with a '/' (meaning that the authority section is omitted from the URI)
then the path is interpreted as a relative path.
On windows, the first component of an absolute path
is a drive specification (e.g. "C:").

The query component of a URI may contain parameters that are interpreted
either by SQLite itself, or by a custom VFS implementation.
SQLite and its built-in VFSes interpret the
following query parameters:

vfs: The "vfs" parameter may be used to specify the name of
a VFS object that provides the operating system interface that should
be used to access the database file on disk. If this option is set to
an empty string the default VFS object is used. Specifying an unknown
VFS is an error. If sqlite3_open_v2() is used and the vfs option is
present, then the VFS specified by the option takes precedence over
the value passed as the fourth parameter to sqlite3_open_v2().

mode: The mode parameter may be set to either "ro", "rw",
"rwc", or "memory". Attempting to set it to any other value is
an error.
If "ro" is specified, then the database is opened for read-only
access, just as if the SQLITE_OPEN_READONLY flag had been set in the
third argument to sqlite3_open_v2(). If the mode option is set to
"rw", then the database is opened for read-write (but not create)
access, as if SQLITE_OPEN_READWRITE (but not SQLITE_OPEN_CREATE) had
been set. Value "rwc" is equivalent to setting both
SQLITE_OPEN_READWRITE and SQLITE_OPEN_CREATE. If the mode option is
set to "memory" then a pure in-memory database that never reads
or writes from disk is used. It is an error to specify a value for
the mode parameter that is less restrictive than that specified by
the flags passed in the third parameter to sqlite3_open_v2().

cache: The cache parameter may be set to either "shared" or
"private". Setting it to "shared" is equivalent to setting the
SQLITE_OPEN_SHAREDCACHE bit in the flags argument passed to
sqlite3_open_v2(). Setting the cache parameter to "private" is
equivalent to setting the SQLITE_OPEN_PRIVATECACHE bit.
If sqlite3_open_v2() is used and the "cache" parameter is present in
a URI filename, its value overrides any behavior requested by setting
SQLITE_OPEN_PRIVATECACHE or SQLITE_OPEN_SHAREDCACHE flag.

psow: The psow parameter indicates whether or not the
powersafe overwrite property does or does not apply to the
storage media on which the database file resides.

nolock: The nolock parameter is a boolean query parameter
which if set disables file locking in rollback journal modes. This
is useful for accessing a database on a filesystem that does not
support locking. Caution: Database corruption might result if two
or more processes write to the same database and any one of those
processes uses nolock=1.

immutable: The immutable parameter is a boolean query
parameter that indicates that the database file is stored on
read-only media. When immutable is set, SQLite assumes that the
database file cannot be changed, even by a process with higher
privilege, and so the database is opened read-only and all locking
and change detection is disabled. Caution: Setting the immutable
property on a database file that does in fact change can result
in incorrect query results and/or SQLITE_CORRUPT errors.
See also: SQLITE_IOCAP_IMMUTABLE.

Windows only: Open the file "data.db" on fred's desktop on drive
C:. Note that the %20 escaping in this example is not strictly
necessary - space characters can be used literally
in URI filenames.

file:data.db?mode=ro&cache=private

Open file "data.db" in the current directory for read-only access.
Regardless of whether or not shared-cache mode is enabled by
default, use a private cache.

file:/home/fred/data.db?vfs=unix-dotfile

Open file "/home/fred/data.db". Use the special VFS "unix-dotfile"
that uses dot-files in place of posix advisory locking.

file:data.db?mode=readonly

An error. "readonly" is not a valid option for the "mode" parameter.

URI hexadecimal escape sequences (%HH) are supported within the path and
query components of a URI. A hexadecimal escape sequence consists of a
percent sign - "%" - followed by exactly two hexadecimal digits
specifying an octet value. Before the path or query components of a
URI filename are interpreted, they are encoded using UTF-8 and all
hexadecimal escape sequences replaced by a single byte containing the
corresponding octet. If this process generates an invalid UTF-8 encoding,
the results are undefined.

Note to Windows users: The encoding used for the filename argument
of sqlite3_open() and sqlite3_open_v2() must be UTF-8, not whatever
codepage is currently defined. Filenames containing international
characters must be converted to UTF-8 prior to passing them into
sqlite3_open() or sqlite3_open_v2().

Note to Windows Runtime users: The temporary directory must be set
prior to calling sqlite3_open() or sqlite3_open_v2(). Otherwise, various
features that require the use of temporary files may fail.